not starting up on 2001 Audi S4

why will my s4 for turn over but not start?

Asked by for the 2001 Audi S4
It could many things, so first check for any codes for a sensor that may be worn out. then see if you have spark, then if you have spark then check for fuel by checking fuel pressure. these are the basic procedures for checking a crank but no start condition. Also does the key icon keep flashing because that would be a security-key-code problem.